Steel plate for lithographic printing



d- 1941- w. N1 ,MlsuRAcA 2,258,956

STEEL PLATE FOR L ITHOGRAPHIC PRINTING Filed Sept. 14, 1938' FIG. 3

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' INVENTOR WILLIAM N. ISURACA ATTORNEY Patented Oct. 14, 1941 UNITEDSTATESPATENT OFF-ICE 2,258,956 S'TEEL PLATE FOR r rr noeaarmc ramWilliam N. Misuraca, Merrick, N. Y., assignor to Misuraca, Inc.,Branchville, N. J., a corporation of New Jersey Application September14, 1938, Serial No. 229,809

4 Claims.

1 formed of a substance having a definite aflinity for grease or agreasy type of marking material, while the non-printing areas of theplate are prepared to accept water so. as to restrict the application ofthe greasy marking material to the printing areas only. At present,the'only metals that have been successfully used for lithographicprinting plates are zinc and aluminum. Although there are many ways inwhich such plates are prepared for printing, one method which is widelyused includes the following steps: (1) Making a print on a grained zincor aluminum plate sensitized with'a dichromated colloid; (2) developingthe print to expose the metal surface in theprinting areas; (3) etchingif desired, and treating the printing areas with an ink receptivesubstance; (4) removing thedichromated colloid coating fromthenon-printing areas; (5) treating the baremetal non-printing areas with adesensitizing acid. solution so as to make such resistance than zinc andaluminum and has the design or printing areas thereof coated with amaterial having substantially as great a wearing life as the harder ormore wear-resistant metal, and the non-printing areas treated with ades'ensitizing solution which will adhere to the harder metal.

In accordance with my invention a grained plate comprising a metalharderor more wearresistant than zinc and aluminum is first coated with alight sensitive solution and exposed to the light through a positive ornegative film. Theexposed plate is then developed so as to eliminateareas receptive to water and, hence, repellant to v grease. I

When plates prepared in this manner, or one of the many modificationsthereof, are used in printing, difiiculties are encountered in retainingthe grease repellant properties of the non-printing areas of the plateand in preventing the wearing probably due'both to friction and to thefact that the plate surface is grained or roughened. Such wearing isalso increased by the fact that the greasy base of the design is notentirely resistthe coating from the unexposed printing areas of theplate. Following this I coat the plate with a resinous material which,when baked at a relatively high temperature, will polymerize to form anextremely hard film; and then remove both the light-hardened sensitivesolution and the resinous material from the non-printing areas of theplate so as to leave the resinous material adhering only to the printingor work areas. In this condition the plate is baked at a suitabletemperature to polymerize the resinous material and render it hardandhighly resistant to the chemical action eration of the followingdescription and the accompanying drawing, in which:

Fig. 1 is a plan view of a finished lithographic plate embodying myinvention;

Fig. 2 is an enlarged vertical sectional view taken substantially alongthe line 2-2 of Fig. 1,

ant; to the corrosiveaction of the acids usually diflicultiesencountered in the use of prior lithographic plates may be overcome byproviding ametal plate which is harder or has greater wear the thicknessof the various layers applied to the plate being exaggerated for thesake of clarity;

Fig. 3 is a greatly. enlarged vertical section through a portion of agrained plate prior to treatment; and

Figs. 4, 5, 6 and .7 are enlarged sectional views, similar to Fig. 2,showing the plate during certain stages of its production.

Referring now to the drawing, it will he noted that in Fig, 3 I haveshown an enlarged-section through a portion of a plate It! the uppersur-' face of which has been roughened or grained, as

indicated at H, by the use of an abrasive which covers the entiresurface with microscopic scratches in a well known manner. The plateused in practicing my invention comprises a metal or alloy such asstainless steel, Monel metal, copper and other special alloys all ofwhich are harder or more wear-resistant than either zinc or aluminum, sothat the grained surface, which is necessary for the retention of wateron the non-printing areas and for the adhesion of the various coatingsapplied during the course of preparation to both printing andnon-printing areas, will have a considerably longer wearing life thanany lithographic plate that has heretofore been successfully used. Themetal employed should alsopreferably be of a type that will not oxidizereadily when subjected to water.

After graining the plate in the usual maimer, the grained surfacethereof is coated with a light sensitive colloidal solution. Thecolloids usually employed are egg albumen, animal glue, gum arabic,etc., and these aretreated with a soluble bichromate or other salt whichis light-sensitive so as to render the colloid substantially insolublein water after exposure. Such a solution is suitably spread over thesurface, as by whirling, to form a thin uniform layer l2 (Fig. 4) whichis free from spots and streaks. When th coating is dry, it is exposed tolight through a positive (or negative) film I3 (Fig. 4). This isgenerally 'done-by placing the plate 10 in a printing frame orphotocomposing machine and printing with the positive film l3 in goodcontact with the sensitized layer l2. In this manner, the sensivecoating [2 is exposed to light only in those areas which correspond withthe clear portions of the positive (or negative) film. Following theprinting, the exposed plate is developed in any suitable manner so thatthose parts of the design which have become hardened by the light willadhere firmly to the surface of the plate and the coating on thoseportions which have not been exposed to light will wash away, leavingthe original metal exposed. In Fig. 5 I have shown the plate at thisstage of the preparation and it will be observed that the coating l2 hasbeen removed from a portion II but is left on the remaining areas I5 ofthe plate. The portion I4 is a part of the design or printing area ofthe plate and is additionally treated in the novel manner now to bedescribed.

When the developed plate has been properly dried, I coat at least theprinting area N thereof with a thin layer l6 of a heat reactivesynthetic resinous composition having the property of polymerizing intoa hard film which'ls resistant to strong acids and alkalis when the filmis baked at an elevated temperature. Such a solution may comprise asuitable phenolic resin varnish, for example, so that it may be appliedwith a brush, spray or any other suitable coating device in the desiredthin layer I6. The following are typical examples of compositions whichmay be used to advantage in practicing this phase of my invention:

Example I Parts by weight Heat reactive phenol formaldehyde resin 35Drying oil acid modified glycerol phthalate resin 10 Solvent naphthaButyl acetate 7 15 Ethyl acetate 15 Butyl alcohol- 1 10 This materialwill form a hard film satisfactory for the purposes of my invention bybaking it at a temperature of about 375 F. for about 22 minutes.

Example II Parts by weight Heat reactive phenol formaldehyde resin Butylaceta Ethyl acetate 25 Butyl alcohol 15 This composition forms a hardfilm when baked at a temperature of about 380 F. for about minutes.

This material also will form a suitable hard film when baked for about25 minutes at a temperature of about 325 F.

I have also found that urea formaldehyde resins, plasticized with alkydresins, and other similarheat hardenable compositions may besatisfactorily used for the layer IS.

The next step in the preparation of the plate is to eliminate allcoating material from the non-printing portions I5 of the plate so as toleave only the thin resinous layer l6 on the printable to heat the plateslightly so as to dry the layer [6 sufliciently that it will adhere tothe surface of the plate when said plate is washed and brushed in theusual manner with a solution in which the lightsensitive layer i2 issoluble. After the grained surface on the non-printing portions l5 ofthe metal plate has been exposed, the plate is baked in a suitable ovento polymerize the resin completely and render the film IE on theprinting area I4 hard and alkali and acid resistant. Such a hardenedfilmwill have a wearing quality substantially equal to that of thegrained surface of a stainless steel plate. The platein this conditionis shown in Fig. '7. Because of the baking necessary to render the filml6 hard and resistant to acids and alkalis, care should be taken toavoid the use of metals which crystallize or become otherwise unsuitableas printing members when subjected to such treatment. The commonhardermetals mentioned above do not exhibit any detrimental change ofstructure when baked at the necessary temperature.

Finally, the plate may be completely prepared for printing by applyingto the bare metal nonprinting portions I5, a thin layer ll (Fig. 2) of asolution which will thoroughly desensitize these parts so that they willretain water and repel grease. A solution which I have foundexceptionally desirable for desensitizing all metals harder than zincand aluminum is a composition comprising chrome alum and gum arabic asdisclosed in my copending application Ser. No. 194,075, filed March 5,19,38. As explained in that application, the chrome alum acts asa'hardener for the gum arabic. so as to render it insoluble withoutexposure or further treatment.

When th finished lithographic printingmember consists of a plate of oneof the harder metcustomary in prior metal plates, these difiiculties maybe obviated; and I consider this a part of my present invention.

From the foregoing description, it will be understood that thelithographic plate embodying my invention will have harder printing andnonprinting areas and consequently a longer useful life thanlithographic plates heretofore known. Moreover, various changes may bemade in the construction and preparation of the plate and certainfeatures thereof may be employed without others, without departing frommy invention or sacrificing any of its advantages.

What I claim is: 1

1. A method of preparing a lithographic printing member, which comprisesgraining the surface of a thin steel plate, applying a light sensitivefilm to the grained surface, exposing said film to light through a filmhaving a design thereon, developing th exposed plate to eliminate thesensitive film from the unexposed printing areas, coating at least thebare printing areas with a heat reacting synthetic resinous compositionwhich may be converted to the insoluble state at atemperature above 300F., removing all coating material from the non-printing areas of theplate, and applying a desensitizing solution including gum. arabic andchrome alum to the non-printing areas of the plate.

2. A lithographic printing member, comprising a stainless steel platehaving a grained surface including printing and non-printing areas, saidprinting areas being coated with a hard set film of resin which does notattack the stainless steel, and said non-printing areas being treatedwith a solution including gum arabic and chromealum.

3. A lithographic printing member comprising a stainless steel plateboth surfaces of which are grained by covering said surfaces with aplurality of microscopic scratches, one of said surfaces having printingand non-printing areas thereon, said printing surfaces being coated witha hard set film of resin of the group consisting of phenol-formaldehyde,urea formaldehyde and vinyl resins, and said non-printing'areas beingtreated with a solution including gum arabic and chrome alum.

4. A method of preparing a lithographic printing member, which comprisesgraining the surface of a thin steel plate; applying a light sensiterialfrom the printing areas of the plate; and

applying a desensitizing solution including gum arabic "and chrome alumto the non-printing areas of the plate.

' WILLIAM N. MISURACA.

